This application claims the priority of Korean Patent Application No. 2003-12697, filed on Feb. 28, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
An apparatus consistent with the present invention relates to a scrolling unit which implements scrolling using two spiral lens disks, thereby increasing light efficiency and decreasing a necessary space for installation, and a color illuminating system and a projection system which use the scrolling unit.
2. Description of the Related Art
Projection systems are divided into a three-panel type and a single-panel type according to the number of light valves which control light emitted from a high-output lamp light source to be turned on or off in each pixel. A single-panel projection system has a smaller optical structure than a three-panel projection system but has only ⅓ of the light efficiency of the three-panel projection system because it splits white light into red (R), green (G), and blue (B) light beams using a sequential method. Accordingly, research and development have been performed to increase light efficiency of single-panel projection systems.
A general single-panel panel projection optical system splits light emitted from a white light source into R, G, and B light beams using a color filter, sequentially transmits the R, G, and B light beams to a light valve, and operates the light valve according to the order of color to form an image. Since such a single-panel optical system uses colors sequentially, the light efficiency of the single-panel optical system is only ⅓ of that of a three-panel optical system. To overcome this problem, a scrolling method has been proposed. According to a color scrolling method, white light is split into R, G, and B light beams, and the R, G, and B light beams are simultaneously transmitted to different positions on a light valve. In addition, because an image can be formed only when all of the R, G, and B light beams reach each pixel, color bars are moved at a predetermined speed using a particular method.
As shown in FIG. 1, in a conventional single-panel scrolling projection system, white light emitted from a light source 100 passes through first and second lens arrays 102 and 104 and a polarized beam splitter array 105 and is split into R, G, and B light beams by first through fourth dichroic filters 109, 112, 122, and 139. For example, the R and G light beams are transmitted by the first dichroic filter 109 and proceed on a first optical path I1, and the B light beam is reflected by the first dichroic filter 109 and proceeds on a second optical path I2. The R and G light beams proceeding on the first optical path I1 are split again by the second dichroic filter 112 such that the R light beam is transmitted by the second dichroic filter 112 and goes straight on the first optical path I1 and the G light beam is reflected by the second dichroic filter 112 and proceeds on a third optical path 13.
The R, G, and B light beams are scrolled by corresponding first through third prisms 114, 135, and 142, respectively. The first through third prisms 114, 135, and 142 are respectively disposed on the first through third optical paths I1 through I3 and rotate at a constant speed so as to scroll R, G, and B color bars. The B and G light beams respectively proceeding the second and third optical paths I2 and I3 are respectively transmitted and reflected by the third dichroic filter 139 and thus mixed. Thereafter, the R, G, and B light beams are mixed by the fourth dichroic filter 122 and then transmitted by a polarized beam splitter 127 so as to form an image due to a light valve 130.
FIG. 2 illustrates a procedure in which the R, G, and B color bars are scrolled by the rotations of the first through third prisms 114, 135, and 142. FIG. 2 shows the movement of color bars formed on a surface of the light valve 130 when the first through third prisms 114, 135, and 142 are rotated in synchronization with one another.
The light valve 130 processes image information according to an on/off signal for each pixel to form an image, and the image is enlarged by a projection lens (not shown) and transferred to a screen.
In the above-described conventional technique, separate optical paths are used for different colors, and therefore, separate optical path compensation lenses are required for the different colors and parts for collecting the split light beams are also required. Since parts for the different colors need to be separately prepared, the volume of an optical system increases. A yield also decreases due to complicated manufacturing and assembling processes. Moreover, driving three motors to rotate the first through third prisms 114, 135, and 142 produces large noise and increases a manufacturing cost compared to a color wheel method using a single motor.
Further, to form a color image using a scrolling method, such color bars as shown in FIG. 2 need to be moved at a constant speed. However, it is difficult to synchronize the light valve 130 and the three prisms 114, 135, and 142 in the above-described structure. Moreover, since the first through third prisms 114, 135, and 142 move in a circle, a scrolling speed is not constant, which may degrade the quality of the image.